1. Field of the Invention
The present invention relates to a clutch friction disc of the kind comprising a support for friction linings, and a hub, which are angularly movable with respect to one another within predetermined limits, the support and the hub being connected by two torsion damping devices, which act in stages, one of which, the first or predamper, being weaker than the second or principal damper. Each of these devices comprise an annular plate, two guiding washers integral with one another and disposed axially on either side of the annular plate, and elastic means for controlling angular movement interposed circumferentially between the annular plate and the washers; as with the associated friction means, the annular plate of the predamper is integral in rotation with the hub, whilst its guiding washers are integral in rotation with the annular plate of the principal damper which is mounted on the hub with a clearance allowing the said fixed angular displacement between the guiding washers integral with the support for the friction linings.
2. Description of the related art
In U.S. Pat. No. 4,603,767 a clutch friction disc of this kind is described in which the predamper is preferably located in the centre of the principal damper between the annular plate and one of the guiding washers. The friction means associated with the predamper comprise a friction washer and a balancing elastic means determining the force of compression between the annular plate and guiding washer; a similar arrangement is also provided in the centre of the principal damper.
It has also been suggested, particularly in French patent No. 2,573,830, that predampers consisting of parts moulded in plastic should be used as friction or sliding surfaces. However, these forms still present definite disadvantages which limit the possibilities of developing them in practice. For instance, the structure of the annular plate of the predamper is considerably weakened by the openings required for the means to fix the guiding washers permanently to one another, and as the friction damping means are all disposed outside the predamper, distributed on both sides of the annular plate of the principal damper, thus introducing multiple elements of friction and balancing, this complicates the construction of the friction disc.
The friction linings of the predamper are also brought into action without the principal damper functioning, which entails a risk of accelerated wear of these surfaces. Moreover, the elastic balancing means act equally at the same time on the friction linings of the predamper and of the principal damper which gives rise to a difficulty in precise regulation of the various frictional effects. In addition, in the absence of automatic compensation for wear, after a certain period of use there is a risk of damping means of the predamper not being in equilibrium with the damping means of the principal damper.
The present invention overcomes these advantages and also permits easier assembly.